This invention relates to a surface elastic wave element having a structure operable with high efficiency.
Recently, there have widely been developed various surface elastic wave (SEW) elements utilizing surface elastic wave which propagates along the surface of an elastic material. These have been developed because (1) surface elastic wave is a surge propagating closely along the surface of a material, (2) its propagating speed is about 10.sup.-5 times of the speed of the electromagnetic wave to allow miniaturization and high concentration of the element and (3) it is expected to realize a new element combined with IC.
FIG. 1 shows an example of conventional surface elastic wave elements in which the reference numeral 1 designates a piezoelectric single crystalline substrate made of LiNbO.sub.3 and 2 and 3 denote comb electrodes provided on the substrate 1, one of the electrodes, 2, for example, serving as an input electrode while the other electrode 3 serves as an output electrode. Surface elastic wave excited through the input electrode 2 propagates along the LiNbO.sub.3 piezoelectric single crystalline substrate 1 and is taken out of the output electrode 3.
The surface elastic wave element with this arrangement, due to high electromechanical coupling coefficient K, when adopted in filters, etc. having comb electrodes, has various advantages like realization of wide-band characteristic, easy matching, reduction of insertion loss, reduction of the number of teeth of the comb electrodes, miniaturization of the element resulting in reduction of production cost. However, such structure of the substrate made from the single material LiNbO.sub.3 has a drawback that the propagation speed and the electromechanical coupling coefficient of the element is substantially fixed in accordance with the direction of crystalline alignment of the surface of the substrate and the progagating direction of the surface elastic wave determined by the crystalline alignment direction.
In order to eliminate the drawback and endow the characteristics with flexibility, there has been proposed a zinc oxide/silicon element, for example. However, the electromechanical coupling coefficient K cannot be improved even by such element as compared with the LiNbO.sub.3 single crystalline substrate.